Release of L-alanine by tumor cells

Culture supernatants from the weakly immunogenic T cell lymphoma L5178Y ESb were found to contain substantial amounts of alanine and lactate at a ratio of about 1:10. Supernatants from cells of the highly immunogenic mutant line ESb-D also contained lactate but only minute amounts of alanine. Moreover, ESb cells converted 14C-labeled glucose or pyruvate into labeled alanine and lactate at a ratio of about 1:10, whereas ESb-D cells yielded only labeled lactate and no detectable alanine. The injection of L-alanine in combination with L-lactate into mice strongly suppressed the capacity of their spleen cells to generate cytotoxic responses. The injection of L-alanine also suppressed the immunogenicity of ESb-D cells, as demonstrated by the generation of cytotoxic activity in vivo and by the in vivo immunization (priming) for secondary cytotoxic responses against ESb-D cells in vitro. Taken together, these experiments suggest the possibility i) that the ESb cells prevent the induction of cytotoxic responses by releasing immunosuppressive alanine, and ii) that the immunogenic mutant ESb-D may have gained immunogenicity by losing this immunosuppressive property.

Release of L-alanine by tumor cells

Culture supernatants from the weakly immunogenic T cell lymphoma L5178Y ESb were found to contain substantial amounts of alanine and lactate at a ratio of about 1:10. Supernatants from cells of the highly immunogenic mutant line ESb-D also contained lactate but only minute amounts of alanine. Moreover, ESb cells converted 14C-labeled glucose or pyruvate into labeled alanine and lactate at a ratio of about 1:10, whereas ESb-D cells yielded only labeled lactate and no detectable alanine. The injection of L-alanine in combination with L-lactate into mice strongly suppressed the capacity of their spleen cells to generate cytotoxic responses. The injection of L-alanine also suppressed the immunogenicity of ESb-D cells, as demonstrated by the generation of cytotoxic activity in vivo and by the in vivo immunization (priming) for secondary cytotoxic responses against ESb-D cells in vitro. Taken together, these experiments suggest the possibility i) that the ESb cells prevent the induction of cytotoxic responses by releasing immunosuppressive alanine, and ii) that the immunogenic mutant ESb-D may have gained immunogenicity by losing this immunosuppressive property.

Glutathione augments the activation of cytotoxic T lymphocytes in vivo

The activation of cytotoxic T lymphocytes (CTL) in vivo was found to be augmented by glutathione if injected i.p. in the late phase but not in the early phase of the response. The effect of glutathione possibly resembles the augmenting effect of 2-mercaptoethanol in lymphocyte cultures.

Demonstration of membrane receptors for human natural and recombinant 125I-labeled tumor necrosis factor on HeLa cell clones and their role in tumor cell sensitivity

Samples of natural and recombinant tumor necrosis factor (TNF) were labelled with 125I by use of Iodobeads and were used to study TNF receptor expression on different HeLa clones. Both labeled preparations retained cytotoxic activity after 125I-labelling and were indistinguishable from their unlabeled counterparts on sodium dodecylsulfate/polyacrylamide gel electrophoresis. They bound specifically to TNF-sensitive cells but not to HeLa clones that were resistant to TNF. The binding of 125I-TNF was competed up to 90% by the addition of non-radiolabeled TNF. The binding reached a half-maximal level at 10 pM and saturation at 100 pM. These concentrations approximated those required for cell destruction. Scatchard analysis of the binding data yielded linear plots suggesting that TNF binds to homogeneous TNF receptor sites. The number of receptor sites ranged between 770 and 2200 sites on TNF-sensitive cells. The surface expression of these TNF receptors appeared to be necessary but not sufficient for the cells to become sensitive against the cytotoxic action of TNF. One of the HeLa clones was found to express the same number of TNF receptors as the most sensitive clone, but was nevertheless resistant to the toxic effect of TNF.

Suppression of cytotoxic T-lymphocyte activation by pyruvate and L-alanine

The activation of cytotoxic T lymphocytes (CTL) in allogeneic mixed-lymphocyte cultures was found to be strongly inhibited if 1-3 X 10(-2) M L-alanine or the structurally and biochemically related substance pyruvate was present in the period from 7 to 19 or from 19 to 120 hr. The cytotoxic response was not inhibited when L-alanine or pyruvate was present during the first 7 hr of the culture period. L-Alanine produced also little or no suppression, if added on Day 3 of the culture. L-Lactate or D-alanine at similar concentrations was not suppressive during the entire culture period. The suppression by pyruvate and L-alanine was strongly reduced by 1 X 10(-4) M adenosine. Adenosine in combination with an interleukin-2 (IL-2)-containing EL-4-cell supernatant was even more effective. Pyruvate and alanine (1-3 X 10(-2) M) also inhibited the DNA synthesis in mixed-lymphocyte cultures on Day 5 by about 50%, but both substances had practically no effect on DNA synthesis in cultures that had been supplemented with an IL-2-containing EL-4 supernatant. They had also no effect on the IL-2-dependent proliferation of several T-cell clones or of concanavalin A-activated thymocytes. These relatively selective regulatory effects of pyruvate and L-alanine may be useful for the analysis of the biochemical pathways during lymphocyte activation and/or for a selective manipulation of the immune response.

Putrescine and its biosynthetic precursor L-ornithine augment the in vivo immunization against minor histocompatibility antigens and syngeneic tumor cells

Putrescine was found to augment strongly the in vivo priming for secondary in vitro cytotoxic responses by small numbers of syngeneic ESb-D tumor cells and MHC-compatible allogeneic cells (minor H-antigens). The cytotoxic response against minor H-antigens in putrescine-treated mice showed the typical MHC-restriction that has previously been observed after immunization with higher cell doses without putrescine. The injection of putrescine had practically no effect on the subsequent in vitro primary cytotoxic response against an unrelated set of allogeneic stimulator cells. A similar augmentation of the in vivo immunization for secondary in vitro responses was achieved with L-ornithine, the biosynthetic precursor of putrescine. A substantial secondary in vivo cytotoxic activity against minor H-antigens was also obtained by application of L-ornithine shortly after the primary immunization.

Antagonistic regulation of cytotoxic T lymphocyte activation by prostaglandin E2 and L-ornithine

Two macrophage-mediated immunoregulatory substances, prostaglandin E2 and L-ornithine, were found to mediate antagonistic effects. Both substances were previously shown to inhibit the activation of cytotoxic T lymphocytes under certain conditions. Our experiments now show that high doses of L-ornithine counteract the inhibitory effect of PGE2, and that PGE2 counteracts the inhibitory effect of high doses of L-ornithine; i.e. both substances can also augment cytotoxic responses in the presence of high concentrations of the other component. The direction of the immune regulatory effects of these substances is, therefore, expected to depend on the endogenous levels of PGE2 and L-ornithine in the individual animal at the site of immunization.

Histamine augments interleukin-2 production and the activation of cytotoxic T lymphocytes

Histamine (0.5 g/kg) was found to augment the activation of cytotoxic T lymphocytes in vivo, if injected in the late phase (day 4) of the response. The production of interleukin-2 in concanavalin A-activated spleen cell cultures was also strongly augmented by 1 X 10(-2) M histamine or by a combination of 2 X 10(-3) M histamine and histaminase (diamine oxidase). This suggests the possibility that the augmentation in vivo is mediated by the oxidized histamine derivative imidazolylacetaldehyde, since diamine oxidase occurs in many tissues. The interleukin-2-dependent proliferation of a T cell clone, on the other hand, was not affected by histamine with or without diamine oxidase. The experiments suggest that histamine supports the late phase of the cytotoxic T lymphocyte response by augmenting the interleukin-2 production.

Regulation of cytotoxic T-lymphocyte activation by L-lactate and pyruvate

The activation of cytotoxic T lymphocytes (CTL) in vivo was found to be strongly augmented by two injections of 0.2 ml 1 X 10(-1) M pyruvate in spite of the relatively high concentration of glucose (approximately 10(-2) M) in the blood. The repeated injection of 1 X 10(-1) M L-lactate, in contrast, was found to suppress cytotoxic responses in vivo. The activation of CTL and DNA synthesis in mixed lymphocyte cultures, on the other hand, was found to be suppressed by pyruvate (1 X 10(-2) M), and was substantially augmented by 1 X 10(-2) M L-lactate. The glucose concentration in the culture medium was also approximately 10(-2) M. Taken together, these results suggest that the utilization of glucose is relatively ineffective and that the respiratory metabolism is a more effective source of energy during the early T cell activation. The results suggest also that the aerobic glycolysis of macrophages and their release of L-lactate may contribute to their function as accessory cells in immune responses. The differences between the in vivo and in vitro results are discussed.

Induction of IL 2 receptor expression and cytotoxicity of thymocytes by stimulation with TCF1

We investigated the role of T cell cytotoxicity inducing factor 1 (TCF1) in the induction of a cytotoxic T cell response. We found that help-deficient thymocyte cultures supplied with saturating amounts of purified IL 2 did not develop CTL in a 5-day culture. The expression of cytotoxicity was dependent on the addition of TCF1 derived from the T cell hybridoma K15. TCF1 also induced proliferation of thymocytes in the presence of IL 2. Only the PNA- thymocyte subpopulation responded to TCF1 with proliferation and cytotoxicity in the presence of IL 2. The monokine IL 1 also induced proliferation in this subpopulation but failed to induce cytotoxicity. IL 1 was further distinguished from TCF1 by inhibition of IL 1-induced but not TCF1-induced proliferation by anti-IL 1 antibodies. In addition, using anti-IL 2 receptor antibodies (AMT 13), we showed that TCF1 in the presence of IL 2 substantially increased IL 2 receptor expression in thymocytes. IL 1 had the same effect on induction of IL 2 receptor expression as TCF1. Because some effects of IL 1 and TCF1 are distinct and some overlap, we discuss whether IL 1 and TCF1 induce different subsets of PNA- thymocytes.

Induction of IL 2 receptor expression and cytotoxicity of thymocytes by stimulation with TCF1

We investigated the role of T cell cytotoxicity inducing factor 1 (TCF1) in the induction of a cytotoxic T cell response. We found that help-deficient thymocyte cultures supplied with saturating amounts of purified IL 2 did not develop CTL in a 5-day culture. The expression of cytotoxicity was dependent on the addition of TCF1 derived from the T cell hybridoma K15. TCF1 also induced proliferation of thymocytes in the presence of IL 2. Only the PNA- thymocyte subpopulation responded to TCF1 with proliferation and cytotoxicity in the presence of IL 2. The monokine IL 1 also induced proliferation in this subpopulation but failed to induce cytotoxicity. IL 1 was further distinguished from TCF1 by inhibition of IL 1-induced but not TCF1-induced proliferation by anti-IL 1 antibodies. In addition, using anti-IL 2 receptor antibodies (AMT 13), we showed that TCF1 in the presence of IL 2 substantially increased IL 2 receptor expression in thymocytes. IL 1 had the same effect on induction of IL 2 receptor expression as TCF1. Because some effects of IL 1 and TCF1 are distinct and some overlap, we discuss whether IL 1 and TCF1 induce different subsets of PNA- thymocytes.

Suppression of cytotoxic T lymphocyte activation by L-ornithine

The effect of L-ornithine on several types of immune reactions was analyzed. L-ornithine was found to suppress the activation of cytotoxic T lymphocytes (CTL) in vivo and in vitro. This suppressive effect was not observed with the structural analogues D-ornithine, L-lysine, or putrescine or with the amino acids L-histidine or L-alanine. The concentration of 9 X 10(-3) M L-ornithine was found to mediate a practically complete suppression of the cytotoxic response in vitro if applied on day 0 or day 1 of the culture, but a comparably weak suppression if applied on day 3. The same concentration of L-ornithine had no effect on the production of the lymphokines interleukin 2 (IL 2) and gamma-interferon (IFN-gamma). This concentration of ornithine had also no substantial effect on several types of proliferative responses, including the allogeneic mixed lymphocyte reaction, the concanavalin A-activated IL 2-dependent proliferation of thymocytes, and IL 2-dependent proliferation of the T cell clone W-2. These observations suggest that L-ornithine inhibits selectively the differentiation of CTL effector cells. By the criteria tested, the immunosuppressive effect of L-ornithine is more selective than that of cyclosporine A, which was previously found to suppress not only the activation of cytotoxic activity but also proliferative responses and the production of the lymphokines IL 2 and IFN-gamma.

Suppression of cytotoxic T lymphocyte activation by L-ornithine

The effect of L-ornithine on several types of immune reactions was analyzed. L-ornithine was found to suppress the activation of cytotoxic T lymphocytes (CTL) in vivo and in vitro. This suppressive effect was not observed with the structural analogues D-ornithine, L-lysine, or putrescine or with the amino acids L-histidine or L-alanine. The concentration of 9 X 10(-3) M L-ornithine was found to mediate a practically complete suppression of the cytotoxic response in vitro if applied on day 0 or day 1 of the culture, but a comparably weak suppression if applied on day 3. The same concentration of L-ornithine had no effect on the production of the lymphokines interleukin 2 (IL 2) and gamma-interferon (IFN-gamma). This concentration of ornithine had also no substantial effect on several types of proliferative responses, including the allogeneic mixed lymphocyte reaction, the concanavalin A-activated IL 2-dependent proliferation of thymocytes, and IL 2-dependent proliferation of the T cell clone W-2. These observations suggest that L-ornithine inhibits selectively the differentiation of CTL effector cells. By the criteria tested, the immunosuppressive effect of L-ornithine is more selective than that of cyclosporine A, which was previously found to suppress not only the activation of cytotoxic activity but also proliferative responses and the production of the lymphokines IL 2 and IFN-gamma.

Effect of L-ornithine on proliferative and cytotoxic T-cell responses in allogeneic and syngeneic mixed leukocyte cultures

The effect of L-ornithine on cytotoxic and proliferative responses in mixed leukocyte cultures has been analyzed. The activation of cytotoxic T lymphocytes (CTL) was strongly inhibited when 9 X 10(-3) M L-ornithine was added at the initiation of the cultures. The CTL precursor cells were not completely and irreversibly inactivated, however, since the cells generated normal cytotoxic activity if resuspended after 6 days in fresh culture medium together with a fresh set of stimulator cells. Experiments in microcultures with nylon-wool-nonadherent T-cell-enriched spleen cells as responder cells and "plastic adherent cells" as stimulator cells revealed that the cytotoxic responses were almost completely suppressed if ornithine was added within the first 20 hr but were only partially suppressed if ornithine was added after 48 hr. Also, ornithine had only a mild suppressive effect on proliferative responses in allogeneic and syngeneic mixed leukocyte cultures. The strong suppressive effect of the cytotoxic response was therefore not explained by a general toxic effect of L-ornithine on the responding cells in the culture. The addition of interleukin 2 (IL-2)-containing EL-4 supernatants did not prevent but rather enhanced the suppressive effect of L-ornithine. This indicated that the inhibitory effect was not (exclusively) expressed at the level of the IL-2-producing helper T cells. Since activated macrophages have been reported to secrete arginase, it appears that L-ornithine may be part of a regulatory circuit that selectively regulates the development of cytotoxic effector T cells.

Augmentation of cytotoxic responses by prostaglandin E2

The cytotoxic-T-lymphocyte activity in the spleen cells after in vivo immunization of C3H mice with allogeneic spleen cells ip was consistently very weak. Substantial cytotoxic responses were obtained, however, when prostaglandins (PGE2, PGE1, or PGI2) were injected ip together with or prior to the immunization. An augmentation of cytotoxic responses against allogeneic stimulator cells was also observed in mixed lymphocyte cultures which were provided with an interleukin 2-containing helper factor. This augmentation was observed when PGE2 was added at the start of the culture but not if added 1 day later. Indomethacin was found to be suppressive in these cultures.

Inhibition of interleukin 2 production by prostaglandin E2 is not absolute but depends on the strength of the stimulating signal

In view of the eminently important role of interleukin-2 (IL-2) in T-cell responses, and in view of reports about immune stimulatory effects of PGE2, we reinvestigated the question whether PGE2 inhibits IL-2 production. It was found that PGE2 does not inhibit IL-2 production in murine spleen cell cultures after optimal stimulation (5 micrograms/ml concanavalin A) but does inhibit at suboptimal stimulation conditions. The failure of PGE2 to inhibit IL-2 production at optimal concanavalin A concentration was demonstrated by two independent IL-2 assays namely by the co-stimulator assay and by the proliferation of IL-2-dependent T-cell clone W-2. Our observations indicated that the inhibitory effect of PGE2 depends on the strength of the stimulating signal. IL-2 production in cultures with 5 micrograms/ml concanavalin A was also not suppressed by PGE1, by prostaglandin D2, thromboxane B2 (T X B2), and prostaglandin F2.

Capacity of different cell types to prime in vivo for secondary in vitro cytotoxic T-cell responses against non-major-histocompatibility antigens

The capacity of several types of cell preparations to induce in vivo a state of memory for a secondary in vitro cytotoxic response against non-major-histocompatibility antigen was markedly reduced (on a per cell basis) by uv-irradiation. This indicated that memory induction requires metabolically active stimulator cells. An "adherent cell preparation" (AC) that was enriched for dendritic cells was among the most effective memory-inducing cell populations; but concanavalin A-activated nylon-wool-nonadherent spleen cells (Con A-NWT) or concanavalin A-activated unfractionated spleen cells (Con A-spl) were on the average equally effective. Normal unfractionated spleen cells (spl) or nonactivated nylon-wool-nonadherent cells (NWT) were markedly less effective on a per cell basis. This pattern of stimulatory activity was in line with the relative stimulatory activity of these cell types in primary cytotoxic responses in the presence of interleukin 2 (IL-2) and also in line with the relative capacity to induce IL-2-dependent proliferation in H-2D-incompatible T-cell populations (cf. W. Dröge et al., J. Immunol. 132, 2749, 1984). These differences in the immunogenic potential and the requirement for metabolically active stimulator cells suggested that these cells stimulated the CTL system directly and not indirectly through antigen processing cells of the immunized host. Nevertheless, the secondary cytotoxic response after injection of low numbers of Con A-spl into H-2 heterozygous recipients, (BALB/c X BALB/b)F1, or into recipients with recombinant H-2 haplotype (A.J) was only preferentially but not exclusively restricted to the H-2 haplotype of the immunizing cell populations. Restriction was considerably more complete when AC were used for immunization.

Mitomycin C-treated or irradiated concanavalin A-activated T cells augment the activation of cytotoxic T cells in vivo

The activation of cytotoxic T lymphocytes (CTL) in vivo after immunization of normal or cyclophosphamide-treated mice with allogeneic cells was strongly augmented by the administration of mitomycin C-treated or irradiated concanavalin A-activated spleen cells (Con A-spl). This effect of the Con A-spl was abrogated by treatment with Anti-Thy 1 antibody plus complement, and was therefore presumably mediated by activated "helper" T cells. (The term "helper" cell is only operationally defined in this context and indicates that the augmenting irradiation resistant T cells are obviously not CTL precursor cells). These observations indicated (i) that even the cytotoxic response against allogeneic stimulator cells suffers in vivo from insufficient "helper" T cell activity, and (ii) that the injection of Con A-spl may serve as a simple procedure to apply this "helper" activity in vivo. This procedure was at least as effective as the repeated injection of interleukin 2 (IL-2)-containing cell supernatants with up to four 30-unit doses of IL-2 per mouse. IL-2-containing cell supernatants were found to mediate similar effects only if injected into the footpads but not intravenously. This was in line with the reported observation that IL-2 has an extremely short half-life in vivo. The injection of Con A-spl was also found to augment the proliferative response in the regional lymph nodes.

Capacity of different cell types to stimulate cytotoxic T lymphocyte precursor cells in the presence of interleukin 2

Plastic-adherent cells enriched for dendritic cells (AC) were found to be among the most potent stimulator cells for the activation of cytotoxic T lymphocytes (CTL) in vitro in the presence of interleukin 2 (IL 2) and a constant second set of allogeneic stimulator cells. Concanavalin A-activated nylon wool-nonadherent spleen cells ( CNWT ), concanavalin A-activated unfractionated spleen cells ( Cspl ), and some variants of the ESb T lymphoma line were equally effective as stimulator cells, however, and provoked a substantial cytotoxic response at concentrations of 10(4) cells per culture or less. In contrast, nonactivated nylon wool-nonadherent spleen cells ( NWT ) or unfractionated spleen cells (Spl) and cells of the P815 mastocytoma, the Meth A fibrosarcoma, and the T cell lymphomas Ly 5178 Eb and ESb did not stimulate cytotoxic responses at these cell concentrations. The strong stimulatory potential of the Cspl preparation was reduced by treatment with anti-Thy-1 antibody plus complement, whereas the stimulatory activity of the AC preparation was resistant to this treatment. All cell types tested expressed class I major histocompatibility antigens. Nonactivated NWT cells, in contrast to the CNWT preparation, showed no detectable staining with anti-I-E or anti-I-A antibodies and also a slightly weaker staining with class I antisera. Experiments with the tumor cell lines revealed, however, that there was no strict correlation between stimulatory potential and density of class I alloantigens or the expression of I-E determinants. Experiments on primary cytotoxic responses in vivo gave similar results. Experiments in cultures with a single set of stimulator cells and I region-compatible responder cells indicated that AC and Cspl or CNWT also have a markedly stronger capacity than NWT to induce IL 2-dependent DNA synthesis.

Capacity of different cell types to stimulate cytotoxic T lymphocyte precursor cells in the presence of interleukin 2

Plastic-adherent cells enriched for dendritic cells (AC) were found to be among the most potent stimulator cells for the activation of cytotoxic T lymphocytes (CTL) in vitro in the presence of interleukin 2 (IL 2) and a constant second set of allogeneic stimulator cells. Concanavalin A-activated nylon wool-nonadherent spleen cells ( CNWT ), concanavalin A-activated unfractionated spleen cells ( Cspl ), and some variants of the ESb T lymphoma line were equally effective as stimulator cells, however, and provoked a substantial cytotoxic response at concentrations of 10(4) cells per culture or less. In contrast, nonactivated nylon wool-nonadherent spleen cells ( NWT ) or unfractionated spleen cells (Spl) and cells of the P815 mastocytoma, the Meth A fibrosarcoma, and the T cell lymphomas Ly 5178 Eb and ESb did not stimulate cytotoxic responses at these cell concentrations. The strong stimulatory potential of the Cspl preparation was reduced by treatment with anti-Thy-1 antibody plus complement, whereas the stimulatory activity of the AC preparation was resistant to this treatment. All cell types tested expressed class I major histocompatibility antigens. Nonactivated NWT cells, in contrast to the CNWT preparation, showed no detectable staining with anti-I-E or anti-I-A antibodies and also a slightly weaker staining with class I antisera. Experiments with the tumor cell lines revealed, however, that there was no strict correlation between stimulatory potential and density of class I alloantigens or the expression of I-E determinants. Experiments on primary cytotoxic responses in vivo gave similar results. Experiments in cultures with a single set of stimulator cells and I region-compatible responder cells indicated that AC and Cspl or CNWT also have a markedly stronger capacity than NWT to induce IL 2-dependent DNA synthesis.

Frequencies of alloreactive and self-restricted cytotoxic T cell precursors during lymphatic regeneration

The previous observation that during lymphatic regeneration precursors for MHC-restricted cytotoxic T cells appear before alloreactive precursors, was re-examined in macroculture and microculture experiments. Our macroculture experiments confirmed the observation that treatment with cyclophosphamide decreases the ratio of alloreactivity vs self-restricted reactivity. This shift in reactivity, however, did not result from a change in the T cell specificity repertoire, but was obviously mediated by regulatory effects in macrocultures. Spleen cells from cyclophosphamide-treated mice had normal ratios of CTL precursor frequencies for the three different specificities tested, but they contained a suppressive activity that inhibited the responses of normal spleen cells in macrocultures. Note Added: After submission of this paper we became aware of the paper of Sihvola and Hurme (J. Immunol. 130:1077, 1983) who also showed that although macrocultures from cyclophosphamide-treated mice were negative for the alloresponse, the same spleen cells showed only a approximately threefold decrease in CTL precursors when analyzed in limiting dilution cultures.

Frequencies of alloreactive and self-restricted cytotoxic T cell precursors during lymphatic regeneration

The previous observation that during lymphatic regeneration precursors for MHC-restricted cytotoxic T cells appear before alloreactive precursors, was re-examined in macroculture and microculture experiments. Our macroculture experiments confirmed the observation that treatment with cyclophosphamide decreases the ratio of alloreactivity vs self-restricted reactivity. This shift in reactivity, however, did not result from a change in the T cell specificity repertoire, but was obviously mediated by regulatory effects in macrocultures. Spleen cells from cyclophosphamide-treated mice had normal ratios of CTL precursor frequencies for the three different specificities tested, but they contained a suppressive activity that inhibited the responses of normal spleen cells in macrocultures. Note Added: After submission of this paper we became aware of the paper of Sihvola and Hurme (J. Immunol. 130:1077, 1983) who also showed that although macrocultures from cyclophosphamide-treated mice were negative for the alloresponse, the same spleen cells showed only a approximately threefold decrease in CTL precursors when analyzed in limiting dilution cultures.

Activation of cytotoxic T lymphocytes requires at least two spleen cell-derived helper factors besides interleukin 2

The dependency of induction of T cell cytotoxicity on lymphokines was studied. 1 X 10(5) nylon wool-purified thymic lymphocytes or 10(4) spleen cells were cultured with TNP-haptenated syngeneic UV-irradiated spleen cells in the presence of a variety of lymphokine preparations. Concanavalin A-induced spleen cell supernatants mediated strong cytotoxic responses in this system. Three other preparations, namely, a partially purified IL 2 preparation from PMA-stimulated EL-4 thymoma cells, a Con A-induced spleen cell supernatant that was absorbed with an IL 2-dependent cell line, and a Con A-induced supernatant that was dialyzed at pH 2 were all ineffective in mediating a cytotoxic response. In reconstitution experiments, cytotoxic responses were only obtained when either the absorbed preparation or the pH 2-treated preparation was mixed with the IL 2 preparation from EL-4 cells. No reconstitution occurred after mixing of the absorbed with the pH 2-treated preparation. pH 2 treatment of the absorbed preparation did not abolish its synergistic effect when added to the IL 2 preparation from EL-4 cells. These results led to the conclusion that activation of cytotoxic lymphocyte precursors requires at least two other lymphokines in addition to IL 2. One T cell cytotoxicity-inducing factor (TCF1) remained in Con A-induced supernatants after absorption with IL 2 receptor-bearing T cell line cells. It was pH 2-resistant and was not found in EL-4 supernatants. A second T cell cytotoxicity-inducing factor (TCF2) was pH 2-sensitive and was found in Con A-induced spleen cell supernatants as well as in interferon-free supernatants of PMA-stimulated EL-4 cells. This activity co-purified with IL 2. It was absorbed by the IL 2-dependent T cell line together with IL 2. IL 2 differs from TCF2 since it is pH 2-resistant.

Activation of cytotoxic T lymphocytes requires at least two spleen cell-derived helper factors besides interleukin 2

The dependency of induction of T cell cytotoxicity on lymphokines was studied. 1 X 10(5) nylon wool-purified thymic lymphocytes or 10(4) spleen cells were cultured with TNP-haptenated syngeneic UV-irradiated spleen cells in the presence of a variety of lymphokine preparations. Concanavalin A-induced spleen cell supernatants mediated strong cytotoxic responses in this system. Three other preparations, namely, a partially purified IL 2 preparation from PMA-stimulated EL-4 thymoma cells, a Con A-induced spleen cell supernatant that was absorbed with an IL 2-dependent cell line, and a Con A-induced supernatant that was dialyzed at pH 2 were all ineffective in mediating a cytotoxic response. In reconstitution experiments, cytotoxic responses were only obtained when either the absorbed preparation or the pH 2-treated preparation was mixed with the IL 2 preparation from EL-4 cells. No reconstitution occurred after mixing of the absorbed with the pH 2-treated preparation. pH 2 treatment of the absorbed preparation did not abolish its synergistic effect when added to the IL 2 preparation from EL-4 cells. These results led to the conclusion that activation of cytotoxic lymphocyte precursors requires at least two other lymphokines in addition to IL 2. One T cell cytotoxicity-inducing factor (TCF1) remained in Con A-induced supernatants after absorption with IL 2 receptor-bearing T cell line cells. It was pH 2-resistant and was not found in EL-4 supernatants. A second T cell cytotoxicity-inducing factor (TCF2) was pH 2-sensitive and was found in Con A-induced spleen cell supernatants as well as in interferon-free supernatants of PMA-stimulated EL-4 cells. This activity co-purified with IL 2. It was absorbed by the IL 2-dependent T cell line together with IL 2. IL 2 differs from TCF2 since it is pH 2-resistant.

Hypothesis on the origin of the strong alloreactivity

The high proportion of alloreactive T lymphocytes and many of the available data on T cell receptors can be explained by one single hypothesis with four basic assumptions: A) The functional induction of T lineage cells in the thymus inherently causes a selection for V-regions that bind to major histocompatibility antigens (MHA). The type of MHA determines the functional pathway of the T cell. B) This process selects with the highest probability for binding sites with high affinity for the self-MHA, yet binding sites with high affinity for non-self-MHA and low affinity for self-MHA will also be selected with a low but finite probability. C) This positive selection for self-MHA binding V-regions is followed by a rigorous selection against self-reactive T cells during the subsequent thymic or post-thymic phase of tolerance induction. D) Most crucial for the hypothesis is, finally, the assumption that the second (negative) selection operates with a higher affinity threshold than the first (positive) selection. The negative selection thus spares T cell clones with low affinity for self-antigens. This provides a strong selective advantage for two major groups of cells, namely alloreactive cells most of which recognize nonself-MHA in complex with nonpolymorphic non-MHA determinants, and cells that recognize nonself-determinants in complex with self-MHA with different degrees of restriction. One of the predictions of this hypothesis is that the proportion of alloreactive cells is relatively small among the T lineage cells that leave the thymus but increases largely during the post-thymic development of the peripheral T cell pool. The hypothesis is not biased in respect to the underlying germ line repertoire of V genes, and is in fact compatible with the simple assumption that T and B cells use the same sets of V genes.

Suppressor cells for in vivo cytotoxic responses--regulation of the in vivo activation of cytotoxic T-lymphocytes by suppressive cells

A significant in vivo activation of cytotoxic T-lymphocytes (CTL) against trinitrophenyl (TNP)-modified autologous cells and of a DNA-synthesis response in the peripheral lymphnodes is observed in cyclophosphamide (CyP) treated mice after skinpainting with trinitrochlorbenzene (TNCB) or after injection of TNP-coupled spleen cells (TNP-Spl) into the footpads. The activation of these responses can be suppressed by the transfer of spleen cells or lymphnode cells from skinpainted normal mice, but not from skinpainted mice that had been pretreated with CyP. Suppressive activity is also induced by injections of TNP-Spl i.p. or trinitrobenzosulfonate (TNBS) i.v. Optimal activation of suppression occurs with 3--4 days. The suppressive activity is antigen-specific at least in respect to its activation. Suppressor cells of this kind also suppress the induction of delayed hypersensitivity (DH) responses and the priming for in vitro secondary responses. However, these two responses are less sensitive to the suppression, and their in vivo activation is accordingly much less restricted with the in vivo activation of DNA-synthesis and primary CTL responses. DH and CMC memory can be activated ty TNCB skinpainting without pretreatment with CyP.